The present invention relates to a vehicle door latch device and, more particularly, to a door latch device in which rattle of a latch to be engaged with a striker is prevented.
As shown in FIG. 8, a conventional door latch device comprises a latch unit A attached to a vehicle door and a striker B fixed to a vehicle body (refer to U.S. Pat. No. 5,141,270). The closed state of a door is held in such a way where a ratchet C of the latch unit A is engaged with a latch D of the latch unit A to keep the engagement between the latch D and the striker B.
The latch D is rotatable to an over-rotated position from an unlatched position by the contact with the striker B. The situation from the unlatched position to the over-rotated position of the latch D is well shown in FIGS. 7 to 10 of U.S. Pat. No. 5,618,068. When the door is moved toward the closed position, the latch D is rotated clockwise in FIG. 8 of the accompanying drawings against the elasticity of a latch spring by the contact with the striker B, and when the latch D rotates up to a half-latched position, a pawl E of the ratchet C is engaged with a half-latch step F of the latch D (refer to FIG. 8 in U.S. Pat. No. 5,618,068). Furthermore, when the latch D reaches a full-latched position, the ratchet C is engaged with a full-latch step G of the latch D (refer to FIG. 9 in U.S. Pat. No. 5,618,068). The latch D is designed to be over-rotatable up to the mechanical rotational limit position exceeding the full-latched position so that the ratchet C can surely be engaged with the full-latch step G (refer to FIG. 10 in U.S. Pat. No. 5,618,068).
When the door is closed, various noises are generated from the door latch device. One of the causes of noise is vibration of the latch D. When the latch D is rotated about a latch shaft H, the latch D vibrates in an axial direction of the latch shaft H to generate rattle noise. If the clearance between the latch D and the latch shaft H is decreased as much as possible, the rattle noise of the latch D can be suppressed. However, a clearance in the neighborhood of zero inhibits a good rotation of the latch D. Furthermore, by providing, to the latch D, a resin projection which comes into sliding contact with a latch body J containing the latch D, the vibration of the latch D in the axial direction of the latch shaft H can also be suppressed. However, the frictional resistance because of the resin projection inhibits a good rotation of the latch D from the unlatched position to the full-latched position.
Furthermore, in many cases, a resin silencer for suppressing the shock noise is attached at the outer peripheral surface of the latch D. The silencer is provided at a part K on the side of the step G, and the silencer suppresses the shock noise generated when the pawl E of the ratchet C collides against the part K of the latch D. However, the silencer cannot reduce the shock noise when the latch D is restored from the over-rotated position (in almost all cases, equal to the mechanical rotational limit position) to the full-latched position and the step G of the latch D collides against the pawl E of the ratchet C. The reason is that the silencer cannot be provided to the step G. If the silencer is provided to the step G, the resin silencer makes the state of engagement between the latch D and the ratchet C unstable. Furthermore, the silencer which may be provided to the step G is extremely worn down by the strong pressure between the latch D and the ratchet C, and therefore, the effect of noise suppression does not last for a long time.
In order to reduce the shock noise when the step G of the latch D collides against the pawl E of the ratchet C, it is effective to weaken the force for over-rotating the latch D. The weakened force reduces the rebounding force applied to the latch D when the latch D is reversed at the mechanical rotational limit position, and consequently, the speed when the step G of the latch D collides against the pawl E is slowed down, and the shock noise is reduced. A rubber stopper L of the latch body J employed in U.S. Pat. No. 5,141,270 is capable of weakening the force for over-rotating the latch D by coming into contact with the striker B. However, the rubber stopper L does not come into contact with the latch D, and therefore, it has no substantial effect for suppressing the vibration of the latch D.
It is an object of the present invention to provide a vehicle door latch device in which the noise generated when the door is closed is suppressed.